1. Field of the Invention
The invention relates to a peristaltic pump for use in medical technology comprising a stator and a rotor, whereby the stator has an occlusion bed which forms the contact area with a tube accommodated within, and the rotor is provided with rolling elements suitable for occluding a tube accommodated between the occlusion bed and the rolling elements.
2. Description of the Related Art
Peristaltic pumps are used in the medical field to convey extracorporeal fluids, or to deliver them in accurate quantities. One use of peristaltic pumps is in dialysis devices, whereby dialysate in the dialysate cycle, dialysis fluid and/or blood needs to be pumped. In a peristaltic pump, a flexible tube is laid along a cylindrical inner diameter, and locally closed or occluded by pressure rollers exerting force radially in an outward direction. The position of the occlusion is changed by the movement of the rollers as they are driven along the tube, thus realizing the pumping of the fluid. An advantage of peristaltic pumps is that they can deliver precise quantities relatively well. Because only the tube comes into contact with the fluid that is conveyed, a peristaltic pump can be cleaned quickly and cost-effectively by replacement of the tube.
Due to the contact between the rollers and the tube, combined with flexing and friction, the tube can be subject to triboelectric charging. Plastic surfaces are most prone to this type of charging. Thus the contact and friction of the surfaces of the stator and the rotor—i.e. the rollers driven by the rotor—with the tube generate and exchange charges, and when the rollers are removed from the tube these charges cannot be equalized with sufficient rapidity, and remain as electrostatic charges on the corresponding surfaces. The charges arise due to the fact that the tube is initially pressed by the pressing force of the rollers against both the occlusion bed, as the corresponding contact surface of the stator, and the rollers. As the rollers move on, each roller lifts off of its section of the tube, with the result that the electrostatic charges described above can be formed on the tube, the occlusion bed and the rollers. Additionally, in the area in which the tube exits the pump, the rollers lift completely off of the tube. When the rotor then turns further, and each roller again comes into contact with the tube in the area in which the tube enters the pump, electrostatic charges which have collected on the roller can be transferred to the tube and thereby cause a corresponding interfering impulse. These charges lead to an electrostatic charging of the tube, and in particular its outer surface. The charge separation is effected according to the triboelectric effect due to the fact that different materials have differing electron affinity, and when such materials are separated the electrons cannot move with sufficient freedom to equalize the charges.
Alongside the generation of charges from the contact between the roller and the tube, electrostatic charges can also be formed between the tube and the occlusion bed. This is because, as the rotor moves on and each roller lifts off of the corresponding section of the tube, the elastic resilience within the tube causes its restitution to its basic cylindrical shape, with the result that the tube is no longer in contact with its occlusion bed over a surface, but only along a line. This is a partial lifting of the tube off of the tube bed, through which electrostatic charges can arise.
In the medical field, diagnosis devices with high-impedance measurement inputs, such as ECG devices, are used, and the measurement results of these devices can be disrupted or distorted by the electrostatic charges on the tube. This problem is known, and the responsible German federal agency BFARM [Federal Institute for Drugs and Medical Devices] recommends that it be alleviated by potential equalization between the devices, i.e. the pump and the diagnosis device, without, however, eliminating the problem. These electrostatic charges appear, as described above, in the form of an electrical interfering impulse, particularly when the rolls are pressed down onto the tube. Dry ambient air can exacerbate this problem. Anti-static sprays are known as an inadequate approach to the elimination of this type of charge. Tubes composed of special materials, e.g. materials containing metal, are also unsuitable for reducing the charges, for reasons of biocompatibility.
Although some ECG devices can filter out these disturbances, and in particular the interfering impulses, by the use of suitable filters, such filters cannot be used in special applications, for example the examination of signals from cardiac pacemakers, because the cardiac pacemaker signals to be measured strongly resemble the interference signals. It is possible, as in U.S. Pat. No. 3,580,983, to attach an electrical grounding cable directly to the tube to prevent charging. Additionally, tube connectors with galvanic contacts for grounding are known from WO 2004/108206 A1. Or, as disclosed in WO 2009/044220 A1, grounding connectors can be attached to the applicable tubes. This prior art has the disadvantage that it addresses less the creation than the transmission and detrimental effects of the charges. The approach to this chosen in U.S. Pat. No. 5,127,907 is that parts that are in motion relative to each other are composed of similar materials. Another disadvantage that is apparent in the known solutions is the additional equipment needed and the additional costs.
The object of the present invention is to prevent or at least reduce disruptive influences of electrostatic charges or electrical impulses from a peristaltic pump upon electrical devices.